11. The sum of the roots of the equation $2 ^ { 2 x } - 8 \times 2 ^ { x } + 15 = 0$ is A 3 B 8 C $\quad 2 \log _ { 10 } 2$ D $\quad \log _ { 10 } \left( \frac { 15 } { 4 } \right)$ E $\quad \frac { \log _ { 10 } 15 } { \log _ { 10 } 2 }$\\